1. Technical Field
The present invention relates to a control device for making retreat traveling possible in a case where a traction motor installed in a hybrid vehicle is broken.
2. Related Art
In the related art, there has been developed a hybrid vehicle which includes an engine and a traction motor (a motor generator) as driving sources for the vehicle, and can allow or interrupt transmission of the driving power of the engine to a power transmission route by a clutch, wherein a generator is connected to the engine. That is, the hybrid vehicle can separately perform driving power generation and electric power generation by the engine and the motor, respectively. This series-parallel type hybrid vehicle can cope with various vehicle driving modes as compared to existing simple driving types such as a series type or a parallel type, and can use the engine and the motor separately or together depending on its traveling state.
However, in some hybrid vehicles each of which is equipped with a plurality of driving sources, in a case where one driving source is broken, control to use any other driving source to drive a vehicle is performed. For example, there is a known vehicle which travels using an engine instead of a motor when the motor is broken. Also, there is a known vehicle which is equipped with a plurality of motor generators, and uses an unbroken motor generator and an engine together such that the vehicle is driven by the engine while using the motor generator to assist the driving power of the engine and generate regenerative electric power. According to this control, even if the motor is broken, traveling performance of the vehicle is secured, and retreat traveling (auxiliary traveling) for moving the vehicle to a repair plant becomes easy (see JP-A-2005-304229 and JP-A-7-067208).
However, when the motor is broken, if there is no fuel for the engine, it is impossible to perform control to use the engine as a driving source. That is, even though regenerative electric power, electric power generated by the generator, and electric power stored in a battery for traveling are abundant, when the motor is broken, retreat traveling of the vehicle may be impossible. Also, even though there is enough fuel, if the fuel supply system and control system of the engine are coincidentally broken, it is impossible to drive the engine, and thus retreat traveling of the vehicle becomes difficult.
Also, motors have characteristics in which they easily obtain torque in a low rotation speed zone; whereas engines have characteristics in which they easily obtain torque in a high rotation speed zone. Meanwhile, in a case of using an engine to drive a vehicle, since an engine rotation speed zone varies depending on the traveling state or load of the vehicle, there is a problem in which the engine may operate in a low rotation speed zone where operation efficiency is low, resulting in a decrease in energy efficiency relative to traveling of the vehicle.
Also, as engines to be installed in hybrid vehicles, types of engines suitable for operations in a high rotation speed zone as described above are often used. In a case of operating such an engine in a low rotation speed zone, if a transmission for giving an appropriate speed reduction ratio does not exist on a power transmission route from the engine to drive wheels, it may become impossible to keep the rotating state of the engine, resulting in an engine stall. That is, in a case of a hybrid vehicle having no transmission as described above, it is practically difficult to start and drive the vehicle by only an engine.
The present invention was made in view of the above described problems, and an object of the present invention is to provide a control device for a hybrid vehicle capable of improving vehicle traveling performance without depending on an engine when a motor is broken. However, the present invention is not limited to that object, and any other inventions which achieve effects which can be derived from components to be described below but cannot be achieved by technologies according to the related art can be regarded as other objects of the present invention.